Lipidos terpenos esteroides

Sterol lipids, such as cholesterol and its derivatives, are an important component of membrane lipids, [43] along with the glycerophospholipids and sphingomyelins. The steroids , all derived from the same fused four-ring core structure, have different biological roles as hormones and signaling molecules . The eighteen-carbon (C18) steroids include the estrogen family whereas the C19 steroids comprise the androgens such as testosterone and androsterone . The C21 subclass includes the progestogens as well as the glucocorticoids and mineralocorticoids . [44] The secosteroids , comprising various forms of vitamin D , are characterized by cleavage of the B ring of the core structure. [45] Other examples of sterols are the bile acids and their conjugates, [46] which in mammals are oxidized derivatives of cholesterol and are synthesized in the liver. The plant equivalents are the phytosterols , such as β-sitosterol , stigmasterol , and brassicasterol ; the latter compound is also used as a biomarker for algal growth. [47] The predominant sterol in fungal cell membranes is ergosterol . [48]